Gas turbine engines generally include a high pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a high pressure turbine. The high pressure compressor, combustor and high pressure turbine sometimes are collectively referred to as the core engine. Such gas turbine engines also may include a low pressure compressor for supplying compressed air, for further compression, to the high pressure compressor.
Normally the compressor efficiency decreases as the compressor inlet corrected flow (along with speed) is reduced beyond about 80% of the design point (DP) flow. Similar efficiency decreases occur with increased inlet corrected flows over about 110% of the DP flow.
It would be desirable to extend the compressor higher efficiency operation beyond the flow ranges described above. It also would be desirable to provide such an extended higher efficiency range without significantly increasing the cost of the engine. At low power, it is desirable to provide improved cycle thermal efficiency and reduced NOx emissions.